PB2239: DOES SIZE MATTER? THREE NEW DELETIONS IN THE HBB GENE CAUSE Β0-THALASSEMIA
Authors: P. Ropero, F. A. González, J. M. Nieto, V. Recasens, Á. Montañés, M. J. Murúzabal, M. Sarasa, C. Fernández, A. Calo, M. Gómez, S. Escribano, H. Martín, S. Rochas, A. Villegas, C. Benavente, G. E. de Eritropatología
Journal: HemaSphere (2022)

Background: Most β-thalassemias are caused by mutations involving one or a limited number of nucleotides within the gene or its adjacent regions. They can be substitutions or deletions, in these cases, the loss ranges from a single nucleotide to 44 nucleotides, so we wonder if the phenotype is due to the size of the deletion or the location of the mutation. Aims: Is it the size of the deletion that determines the phenotype of β0-thalassemia? To elucidate this, we present three new deletions in the β-globin gene that cause β0-thalassemia. Methods: The hematological parameters were determined with an automated cell counter; The Hb A2 and Hb F levels were measured by performance liquid chromatography. Hemoglobins were analyzed by capillary zone electrophoresis (Sebia Capillarys Flex system) and ion exchange HPLC (BioRad Variant II β-thalassemia Short Program). Molecular characterization was performed by automatic Sanger sequencing. The screening of common α-thalassemia point mutations and deletions in the world (21 in total) were carried out using multiplex PCR followed by reverse-hybridization with a commercial Alpha-Globin StripAssay kit Results: Three new mutations have been characterized: 1) 1 bp deletion [CD61 / 62 (–G)] [HBB: c.186_187delG]; 2) 25 bp deletion [HBB: c.93-22_95del] and 3) 105 bp deletion [IVS-2-nt767-CD111] [HBB: c.316-84_333del]. Image:Summary/Conclusion: These three mutations present a phenotype consistent with β0-thalassemia, supported by the hematological parameters that correlate the degree of β globin chain synthesis reduction. Thus, all of them presented anemia with hemoglobin levels between 8.3 g/dL and 13 g/dL, the most severe corresponding to the girl with hepatitis A, with this greater severity probably being related to the hepatitis. Microcytosis evaluated by mean corpuscular volume was more marked in the family carrying the 105 bp (57.8 fL) deletion, while the single base deletion resulted in a MCV of 65.8 fL. About to the mean corpuscular hemoglobin levels to determine hypochromia, the values furthest from the normal are observed to coincide with the most extensive deletion, even though in all patients the MCH was lower than usual for heterozygous β-thalassemia, while Hb A2 levels were higher, close to 6%, although similar in all three types of mutation. Nonetheless, the values do not differ enough between them to think that the size of the deletion determines the phenotype. These three new mutations show that it is not the size of the deletion that determines the phenotype in β-thalassemia, but rather the location of the deletion, and which process it affects among the stages of gene expression. Two of the three mutations have been identified in non-Spanish patients (Dominican and Moroccan). This confirms the increase in patients with this type of pathology as well as the use of health services as a reflection of immigration for work reasons along with refugees due to war conflicts, in addition to adoptions of children from areas where these pathologies are frequent.